Formula to Calculate Effective Tax Rate

Understanding Car Loan Amortization and Your Monthly Payments

When financing a new or used vehicle, understanding how your loan is structured is crucial for budgeting and long-term financial planning. A car loan is typically an amortized loan. This means your monthly payments are fixed over the life of the loan, but the portion of that payment allocated to principal versus interest changes over time.

In the beginning of your loan term, a larger percentage of your monthly payment goes toward paying off interest. As the principal balance decreases, the amount of interest charged each month also decreases, meaning more of your fixed payment goes toward reducing the actual debt (the principal).

How Your Monthly Car Payment is Calculated

Your auto loan payment depends on several key factors. Understanding these will help you use our amortization calculator more effectively:

  • Vehicle Price: The negotiated purchase price of the car, including taxes and fees.
  • Down Payment & Trade-In: Any cash you pay upfront or the equity from trading in an old vehicle reduces the total amount you need to borrow. A larger down payment significantly reduces total interest paid.
  • Interest Rate (APR): The annual percentage rate charged by the lender. Even a small difference in the rate can amount to hundreds or thousands of dollars over a 5 or 6-year loan term. Rates depends on your credit score and current market conditions.
  • Loan Term: How long you have to repay the loan, typically expressed in months (e.g., 36, 48, 60, 72, or even 84 months). While longer terms lower your monthly payment, they increase the total interest paid because you are borrowing the money for longer.

Why Use an Amortization Calculator?

While knowing your monthly payment is important for your monthly budget, an amortization calculator reveals the "true cost" of the car. It shows you exactly how much you will pay in total interest over the life of the loan. It can be shocking to see that on a long-term, high-interest loan, you might end up paying significantly more than the car's sticker price once interest is factored in.

Use the calculator below to experiment with different scenarios. See how increasing your down payment by $1,000, shortening the term by 12 months, or securing a slightly lower interest rate impacts both your monthly obligation and your total long-term cost.

Car Loan Amortization Calculator

36 Months (3 Years) 48 Months (4 Years) 60 Months (5 Years) 72 Months (6 Years) 84 Months (7 Years)

Loan Summary

Estimated Monthly Payment:
Total Principal Loaned:
Total Interest Paid:
Total Cost of Car (Loan + Interest):
function calculateCarLoan() { // Get input values var vehiclePrice = parseFloat(document.getElementById('vehiclePrice').value) || 0; var downPayment = parseFloat(document.getElementById('downPayment').value) || 0; var tradeInValue = parseFloat(document.getElementById('tradeInValue').value) || 0; var interestRate = parseFloat(document.getElementById('interestRate').value) || 0; var loanTermMonths = parseInt(document.getElementById('loanTermMonths').value) || 60; // Calculate Principal var principal = vehiclePrice – downPayment – tradeInValue; var resultDiv = document.getElementById('amortizationResult'); // Edge case handling if (principal <= 0) { resultDiv.style.display = 'block'; document.getElementById('resultMonthlyPayment').innerHTML = "$0.00"; document.getElementById('resultTotalPrincipal').innerHTML = "$0.00"; document.getElementById('resultTotalInterest').innerHTML = "$0.00"; document.getElementById('resultTotalCost').innerHTML = "$" + (downPayment + tradeInValue).toFixed(2) + " (Paid Upfront)"; return; } if (vehiclePrice <= 0 || interestRate < 0 || loanTermMonths <= 0) { alert("Please enter valid positive numbers for vehicle price, interest rate, and term."); return; } var monthlyPayment = 0; var totalInterest = 0; var totalCost = 0; // Amortization Calculation if (interestRate === 0) { monthlyPayment = principal / loanTermMonths; totalInterest = 0; } else { var monthlyRate = (interestRate / 100) / 12; // Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ] var mathPower = Math.pow(1 + monthlyRate, loanTermMonths); monthlyPayment = principal * ((monthlyRate * mathPower) / (mathPower – 1)); totalInterest = (monthlyPayment * loanTermMonths) – principal; } totalCost = principal + totalInterest; // Formatting currency strings var formatter = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD', }); // Display Results resultDiv.style.display = 'block'; document.getElementById('resultMonthlyPayment').innerHTML = formatter.format(monthlyPayment); document.getElementById('resultTotalPrincipal').innerHTML = formatter.format(principal); document.getElementById('resultTotalInterest').innerHTML = formatter.format(totalInterest); document.getElementById('resultTotalCost').innerHTML = formatter.format(totalCost); }

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